The present invention generally relates to an assembly for positioning a thermogravimetric furnace and, in particular, relates to such an assembly having means for selectively moving the thermogravimetric furnace to either a sample loading position or a furnace cooling position.
Thermogravimetric analyzers are instruments designed to detect weight changes in a sample as it is subjected to preselected temperature changes. In general, such an analysis is carried out by first placing a sample in a sample tray which is suspended from one arm of a precision balancing mechanism. The sample is then introduced into a furnace the temperature of which is controllable and preselectable. Usually in such an analyzer, a portion of the furnace is movable and the sample tray is fixed, at least with respect to the movable portion of the furnace. The temperature of the furnace is then varied over time in a preselected fashion. This variation is generally referred to as a temperature profile and the weight of the sample is monitored throughout the profile. The most common method of analysis includes a continuous weight detection of the sample throughout the temperature profile. However, in some instances, only the weight of the residue at the end, usually at high temperatures, of the profile is of interest. In any event, the results of such an analysis are usually recorded via a chart recorder whereon the sample weight is plotted against the temperature during the profile.
In conventional thermogravimetric analyzers, after a temperature profile on a particular sample has been performed, the movable portion of the furnace is usually lowered away from the sample tray. This lowering is most frequently performed by manually grasping the lower portion of the furnace housing and moving it downwardly away from the suspended sample tray. This, of course, is extremely hazardous since the temperature of such furnaces can reach more than 1500.degree. C. and such manual manipulation of the furnace can cause severe burns.
Another drawback common to conventional thermogravimetric furnaces is the prolonged time required for cooling the furnace before the next analysis can be performed. For example, since the furnace assembly reaches such high temperatures, which are usually at the end of the temperature profile, the cooling time between samples can be quite long. One common goal of analytical instrument designers is to have the total time of a sample analysis depend primarily on the actual analysis time plus the time required for changing samples. The present form of thermogravimetric analysis, due to the required cooling, entails considerable delays between samples.